Reland "[AArch64] FMV support and necessary target features dependencies."

This relands commits e43924a7,
a43f3614,
bf94eac6 with MSan buildbot
https://lab.llvm.org/buildbot/#/builders/5/builds/30139
use-of-uninitialized-value errors fixed.

Differential Revision: https://reviews.llvm.org/D127812